The present invention relates generally to power generating systems connected to a grid and, more particularly, to control of a wind power generating system.
Wind turbine generators are regarded as environmentally friendly and relatively inexpensive alternative sources of energy that utilize wind energy to produce electrical power. A wind turbine generator generally includes a wind rotor having turbine blades that transform wind energy into rotational motion of a drive shaft, which in turn is utilized to drive a rotor of an electrical generator to produce electrical power. Modern wind power generation systems typically take the form of a wind-farm having multiple such wind turbine generators that are operable to supply power to a utility system.
Some wind turbine generators have a variable frequency operation and require a variable frequency power electronic converter to interface the wind turbine generator output with the utility grid. In one common approach, the wind turbine generator output is directly fed to a power electronic converter where the generator output frequency is rectified and inverted into a fixed frequency as needed by the utility system.
One of the challenges associated with such systems is control of wind turbines in the event of a weak and/or resonant grid connection. For example, to compensate for a weak grid connection use of series compensation, such as a series capacitor bank, is one means of increasing transmission capability in the grid, but this has potential limitation. Series compensation may lead to sub-synchronous resonance modes that can couple to the power electronic converter controllers causing control instability. Resonant mode coupling challenges may also occur at super synchronous frequencies due to the interaction of distributed shunt capacitance and line inductance in the network.
Therefore, it is desirable to determine a method and a system that will address the foregoing issues.